The present invention provides a method for preventing tissue injury caused by tissue hypoxia, comprising administering a compound that inhibits signal transduction by inhibiting cellular accumulation of a linoleate-containing phosphatidic acid (PA) through an inhibition of the enzyme LPAAT (lysophosphatidic acyltransferase).
Acute lung injury, manifested clinically as the Adult Respiratory Distress Syndrome (ARDS) occurs in more than 50% of patients following severe injury and blood loss. ARDS is characterized clinically by decreasing lung compliance and severe impairment of oxygen diffusion (Hammerschmidt et al., Lancet 1:947, 1980; Moore et al., J. Trauma 31:629, 1991; Pepe et al., Am. J. Surg. 144:124, 1982; and Baker et al., Am. J. Surg. 140:144, 1980). Histologic changes in the lungs which are present in this setting include neutrophil and mononuclear infiltrates, interstitial edema, intraaveolar hemorrhage, and fibrin formation. In injured patients, increased plasma levels of proinflammatory cytokines, such as IL-6 and IL-8, as well as evidence of endothelial activation, as shown by elevated circulating titers of soluble intracellular adhesion molecules (sICAM), are found within one hour of blood loss and trauma. Bronchoalveolar lavages obtained from patients with ARDS contain elevated titers of IL-1xcex2 and TNFxcex1. Also, release of proinflammatory cytokines, such as IL-1 and TNFxcex1 is increased after blood loss (Abraham et al., Circ. Shock 25:33, 1988; Meldrum et al., J. Surg. Res. 51:158, 1991; and Ertel et al., Immunology 74:290, 1991). Studies examining the 4 hour period immediately following hemorrhage demonstrated increased levels of mRNA for proinflammatory cytokines, including IL-1xcex1, IL-1xcex2, TNFxcex1, IL-6 and IFN-xcex3, among cells isolated from mucosal sites (e.g., lungs and intestines) but not among splenocytes or peripheral blood mononuclear cells (Shenkar and Abraham, Lymphokine Cytokine Res. 12:237, 1993). It has been postulated that increased local production of proinflammatory cytokines may contribute to lung injury in this setting. Blood loss is a central factor in the pathophysiologic instability that follows trauma, and has been associated with alterations in macrophage, T cell and B cell function. Hemorrhage does not result in changes in absolute or relative numbers of T cell or B cell subsets in the spleen, lymph nodes, blood or iung (Abraham and Freitas, J. Immunol. 142:899, 1989; Robinson and Abraham, J. Immunol. 145:3734, 1990; Abraham et al. Cell. Immunol. 122:208, 1989; and Robinson et al., Clin. Exp. Immunol. 88:124, 1992).
It is possible that the local ischermia and/or hypoxia created by redistribution of blood flow in visceral (splanchnic) organs such as the gut (particularly the small intestine) and kidney are responsible for induction of the cytokine cascades, which in turn, result in distal organ injury. Evidence exists demonstrating that absolute and relative blood flow levels within these organs fall within minutes of volume shifts, hemorrhage, or induction of other causes of shock (textbook Hypertension). There is, therefore, a need in the art for compounds which (1) prevent initial production of proinflammatory cytokine mediators in response to decreased perfusion and (2) prevent redistribution of microcirculation induced by these proinflammatory cytokine mediators.
In severely injured patients, serum levels of IL-6 and IL-8 are increased within one hour or injury, but do not appear to predict which patients will develop ARDS (Hoch et al., Crit. Care Med. 21:839, 1993). No detectable IL-1xcex1, IL-1xcex2, orendotoxin was found in patient samples obtained over 5 days post-injury in these patients (Hoch et al., infra.). Moreover, plasma levels of TNF are rarely increased following severe injury and there does not appear to be any correlation between the presence or amount of TNFxcex1 and the development of ARDS or organ system dysfunction.
Based upon experiments ongoing which examine the biochemical events following severe injury with blood loss and resulting tissue hypoxia, even if treated medicinally with fluids and/or blood products still results in inflammatory changes in the lungs and other organs.
Neutrophils are important for host-defense against bacterial and other infections. This is suggested as a consequence of observations that there is an increased infections seen in patients with insufficient numbers of neutrophils or with neutrophils with genetically determined abnormalities (e.g., chronic granulomatous disease). Antibiotics are available to treat infections (i.e., be directly cytotoxic to the infectious agent), but there are no specific therapies available to treat septic shock or the compounding organ dysfunction that follows from septic shock or other causes of tissue hypoxia/ischemia. Therefore it may be necessary to risk decreasing neutrophil function (as direct cytotoxic agents against the pathogen) to prevent fatal lung injury and other organ dysfunction.
Cystic fibrosis (CF) is a lethal hereditary disorder caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CFTR gene product is a 168 kD glycosylated membrane protein that functions as a chloride channel regulated by cytoplasmic protein kinases (Riordan et al., Science 245:1066, 1989). Although the link between mutations in the CFTR gene and the pathogenesis of CF are not understood, the lethal clinical manifestations of CF are related to a thick, infected mucus and chronic neutrophil-dominated inflammation of the epithelial surface of the airways. A large number of neutrophils place the airway epithelium in jeopardy consequent to exposure to potent neutrophil mediators, including neutrophil elastase (NE), and reactive oxygen species, and a variety of cytokines (Sibille and Reynolds, Am. Rev. Respir. Dis. 141:471, 1990; and McElvaney et al., Lancet 337:392, 1991). Although critical to host defense, neutrophils cause progressive damage to airway epithelium by virtue of their potent mediators, most significantly NE. Not only can NE damage epithelial cells by direct proteolytic effects, but it can also hinder host defense by interfering with ciliary clearance, increasing mucus production, cleaving immunoglobutin and complement, and by impairing phagocytosis and killing of Pseudomonas aeruginosa by neutrophils. The fluid lining the respiratory epithelium in CF contains large numbers of activated neutrophils and active NE, and the NE in CF is capable of inducing bronchial epithelium cells to express the gene for IL-8 and release neutrophil chemotactic activity as properties of IL-8 (Nakamura et al., J. Clin. Invest. 89:1478, 1992). Neutrophils in the thick mucus are rendered hypoxic. Therefore there is a need in the art to find a therapeutic compound capable of inhibiting IL-8 signaling and thereby provide treatment for CF.
Hypoxic injury generates oxidative injury. For example, serum antioxidants may be predictors of ARDS in sepsis patients. At an initial diagnosis of sepsis (6-24 hr before development of ARDS), serum manganese superoxide dismutase concentration and catalase activity were higher is a study of patients (6) who subsequently developed ARDS as compared to patients (20) who did not develop ARDS (Leff et al., Lancet 341:777, 1993). Accelerated intravascular generation of oxygen radicals from stimulated neutrophils, circulating xanthine oxidase, and other sources have been implicated in the pathogenesis of sepsis and ARDS (Repine, Lancet 339:466, 1992). Moreover, in vitro, exposure to decreasing oxygen tensions progressively increased xanthine dehydrogenase (XD) and xanthine oxidase (XO) activities over 48 hr in cultured pulmonary artery endothelial cells without altering XD/XO ratios. Oxygen tension negatively modulates XO and its precursor XD, and was associated with an increase in release O2xe2x88x92 (Terada et al., Proc. Natl. Acad. Sci. USA 89:3362, 1992). This connection to hypoxia and multiple organ failure or dysfunction is further strengthened by a clinical trial report that recombinant human superoxide dismutase administered in a placebo-controlled trial attenuated multiple organ failure, shortened intensive care therapy, and decreased the release of inflammatory mediators (Marzl et al., J. Trauma 35:110, 1993).
The present invention provides a method for inhibiting hypoxic injury (comprising hypoxia and reoxygenation) to tissues and organ dysfunction, comprising administering a compound that inhibits signal transduction through cellular accumulation of linoleate-containing phosphatidic acid (linoleoyl-PA). Preferably, the compound is an organic molecule that inhibits generation of linoleoyl-PA that exerts its activity through inhibition of lysophosphatidic acyltransferase (LPAAT). Hypoxic injury is manifest as: (1) multiorgan dysfunction following shock caused by hemorrhage, severe cardiac dysfunction, severe burns, or sepsis, (2) CNS tissue injury following occlusive cerebrovascular accidents (stroke), (3) cardiovascular tissue injury following myocardial infarction, (4) organ dysfunction following transplantation of kidney, liver, heart, lung, or bowel, (5) organ damage following vascular surgery in any site, such as coronary artery, cerebral vasculature, or peripheral angioplasty, (6) high altitude pulmonary edema (altitude sickness), (7) acidosis, such as diabetic acidosis, drug-induced acidosis (e.g., salicylate poisoning), and renal acidosis, (8) prevention of organ transplant rejection due to hypoxia, or (10) hypoxia-mediated neurodegenerative diseases, such as Parkinsons disease, Huntington""s disease, Alzheimer""sdisease and ALS(Amyotrophic Lateral Sclerosis). Hypoxic injury to neutrophils is also a component of cystic fibrosis, therefore, the present method includes treatment (to prevent further progression) of cystic fibrosis, comprising administering an effective amount of a compound that can effectively inhibit LPAAT activation in response to a hypoxia and reoxygenation.